1. Field of the Invention
The present invention relates to improved polymeric nitrile packaging compositions. More particularly, the present invention relates to a process for preparing improved packaging materials for foods, medicines and other related substances from molten nitrile polymers. The process comprises having styrene oxide in intimate contact with the molten polymer during the forming of the packaging materials.
2. Description of the Prior Art
In recent years it has been discovered that certain polymeric nitrile resins are especially suitable for packaging applications because of their excellent water and oxygen barrier properties. Such polymers are described at length in U.S. Pat. Nos. 3,451,538 and 3,615,710, among others. Even more recently it has been discovered that although such nitrile polymers have excellent barrier properties they may be unsuitable for certain packaging applications because they contain trace, though detectable, amounts of hydrogen cyanide (HCN) which may be extracted by and impart a taste to the contents of the package. The amount of HCN in such nitrile polymers will vary with the nitrile monomer, the total nitrile content of the polymer, the polymerization method used to prepare the polymer, the processing and thermal history of the polymer and other factors. Moreover, it has been found that the amount of extractable HCN in nitrile polymers may be increased after the polymer has been subjected to forming operations wherein the polymer has been heated in order to soften and/or melt the polymer prior to forming it into shaped articles, unless precautionary steps are taken.
The trace amount of extractable HCN present in such nitrile packaging materials is very low and presents no known health or safety problems. In fact, the amount of extractable HCN in such nitrile polymers is lower than that found in many foods. In this regard it should be noted that HCN is a natural component in many foods and many other foods such as cereals, cocoa, ham, bacon and sausage, which are fumigated with HCN (prussic acid), are permitted to contain from 50 to 200 parts per million of HCN. (See the Food Additive Regulations of the FDA (Page 31, Subpart D, Paragraph 121,1072) as published in the Federal Register: Dec. 23, 1965; 30 F.R. .15912 and the 1962 Public Health Service Publication 956 "Drinking Water Standards.")
However, as stated above, the HCN in certain nitrile packaging materials may, in certain instances, be extracted and impart a taste to the contents of the package. The problems of HCN extraction as it affects taste, is of concern in the packaging of beverages which are in prolonged intimate contact with the container. In these packaging applications the probability of HCN extraction is very high.
Thus, there exists in the art a need for improved nitrile polymer packaging materials which are substantially free of extractable HCN. This need is fulfilled by the present invention which significantly reduces the amount of extractable HCN in nitrile packaging materials. More particularly, the present invention is especially suitable for the preparation of packaging materials such as bottles, cans, jars, etc., which are used in the packaging of beverages, including carbonated beverages, where the probability of HCN extraction is very high.